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Old 01-14-2025, 08:51 AM   #1
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why does water tank get full when on town water?

My latest issue on my 07 Monaco Diplomat 40. I hook up the hose and turn the lever to town water. At the time I did this 2 days ago the water tank was about 1/2 to 2/3 full. This morning I noticed the water tank was showing it was full?? This happend a few days ago as well. My only guess is that even with the lever at town water a small amount is going into the water tank. That is just my guess however but can't figure out how else it could happen.

Has anyone seen this before and if so what was cause and solutions?
Thx,
Roger
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Old 01-14-2025, 08:53 AM   #2
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why is water tank filling if on town water?

My latest issue on my 07 Monaco Diplomat 40. I hook up the hose and turn the lever to town water. At the time I did this 2 days ago the water tank was about 1/2 to 2/3 full. This morning I noticed the water tank was showing it was full?? This happend a few days ago as well. My only guess is that even with the lever at town water a small amount is going into the water tank. That is just my guess however but can't figure out how else it could happen.

Has anyone seen this before and if so what was cause and solutions?
Thx,
Roger
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Old 01-14-2025, 08:54 AM   #3
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Either a leaking valve in the water pump or the city/fill valve is leaking. Try turning that valve back and forth a couple of times to see if it will seal. If it is the wter pump you may need to replace the seals in the pump. There are kits available for them and they aren't too hard to repair.
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Old 01-14-2025, 08:59 AM   #4
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David,
Thx for the reply. I can understand moving the lever back and forth but confused about the pump? Doesn't the lever cause the water to bypass the water pump? I turn the pump off when on town water so maybe Im confused on how the system works?
Roger
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Old 01-14-2025, 10:23 AM   #5
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The lever is actually a 3 way valve that switches the water direction. On city water it is suppose to bypass the pump.

There is a check valve in my system that I had to change.

I have a Swan valve, the check valve is on the left. I took the whole thing out but found that I could have changed the check valve in place. There is piping behind it with thrumb screw type fittings, just had to reach up behind to disconnect.
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Old 01-14-2025, 10:24 AM   #6
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Here's a picture
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Name:	City Water Valve.jpg
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Old 01-14-2025, 10:46 AM   #7
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When on 'City Water' the fresh water tank can fill/overflow due to:
*fill valve leaking thru
*internal check valve of on-board pump leaking thru

Fill valve...thru city water source OFF
then exercise the valve between fill and city water positions
Otherwise you might have to replace it


Sometimes just running the pump and using the water in the fresh water tank can clear/allow pump check valve to close

Which one?
If you have access to the suction line going to water pump
Disconnect it
Turn on 'City water' and check if water flows back out of pump

If you have flow out of pump then pump check valve is not closing fully
*replace internal check valve assembly
*OR install an in-line check valve in pump suction line

If no water backflowing thru pump then FILL Valve would be leaking thru
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Old 01-14-2025, 10:50 AM   #8
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I guess I've never seen a valve like the swan valve, but then I live a pretty secluded life. All the rvs I've had did not have that. Mine just had a two-way valve and the check valves in the pump stopped the water from going back to the tank, the same way they held the pressure in the system in the system when the pump shut off. So, the op has to figure what system he has.

https://www.grainger.com/product/SHU...7fb4b71b4d0ba5

Here is an example of the repair kit.
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Old 01-14-2025, 10:52 AM   #9
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On-board pump discharge and City Water inlet feed the SAME cold water lines which then feeds the how water heater

City water/Fill valve just swaps city water inlet feed to Supply RV Cold line OR Fill the fresh water tank

Water pump is not bypassed in either position
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Old 01-14-2025, 10:59 AM   #10
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On other possibility, but a stretch-

Do you have a hot water diverter on the shower?

If the diverter is set to divert the water back to the tank, it would allow the city water to fill the tank. Depending on how the diverter is plumbed, some require the shower hot water valve to be open, some don't.

But I would never second guess Old-Biscuit.
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Old 01-14-2025, 11:44 AM   #11
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To elaborate on Old-Biscuit's response IF this is a check valve problem in the water pump:

There may be a check valve inside the water pump that keeps City Water from flowing backward through the pump and filling the fresh water tank. Sometimes you can clear a check valve that is stuck open by:

- Turn City Water off.

- Turn the water pump on.

- Open a faucet full blast for a few seconds and then close it. Repeat a few times.

- Turn the water pump off.

- Turn City Water back on.

If you're lucky the sudden rush of water through the pump will unstick that check valve or clear whatever is holding it open.

If not, many people simply install a check valve on the water pump intake to take the place of the internal one instead of buying a new pump. This one is reported to work well but I've never needed it, yet.

https://www.amazon.com/gp/product/B0...KIKX0DER&psc=1

If you switched to running solely off the water pump to use up the water in the fresh tank and you hear the water pump cycling on and off that will confirm a stuck check valve (assuming there is no leak inside).

With a stuck check valve the water pump will cycle on and off. As the pressure in the RV water lines decreases because water is slowly leaking backward into the fresh tank the pump will turn on to bring the pressure back up.

--------------------

A workaround is available if you have a winterization valve on the water pump inlet.

The winterization valve is on the inlet side of the water pump. When the valve is in the usual position the valve allows the water pump to suck water out of the fresh water tank. When the valve is turned to the other position, the water pump inlet is switched from the fresh tank to a short piece of water hose.

When winterizing, you remove the cap from the end of the short hose and place it in a jug of RV antifreeze. The water pump sucks the antifreeze out of the jug and into the water system.

The workaround: Because the winterization valve disconnects the water pump from the fresh tank, you can temporarily move the winterization valve to the winterization position AND assure the cap is on tight.

When City Water tries to flow backwards through the pump it cannot go into the fresh tank; it goes into that short piece of capped-off hose. Of course, if you need to use the water pump you need to remember to change the winterization valve back to the normal position.

Make sense?

Ray
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Old 01-14-2025, 04:40 PM   #12
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Thanks for the info. So if I understand correctly the check valve on the water pump prevents town water from going into the water tank if the town water is selected. So Im assuming that if I remove the water pump assembly I can replace the faulty valve. Make sense?
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Old 01-14-2025, 09:51 PM   #13
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Quote:
Originally Posted by rogerlamb View Post
Thanks for the info. So if I understand correctly the check valve on the water pump prevents town water from going into the water tank if the town water is selected. So Im assuming that if I remove the water pump assembly I can replace the faulty valve. Make sense?
Most have check valve replacement kits

IF...that is the problem

What brand/model is the pump?


Before replacing/repairing pump.........verify that pump check valve is the reason City Water is getting into fresh water tank and not the 'fill' valve
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Old 01-14-2025, 10:20 PM   #14
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This is a very common problem. The internal check valve in the water pump is leaking by allowing city water to leak into tank via the pump. Easy solution is to buy a simple check valve at a home store and install it between the pump and tank. Something similar to this: https://www.homedepot.com/p/SharkBit...UGNlHqXk&gQT=1

Be sure not to install it backwards!
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